POINT OF VIEW Eur. J. Entomol. 96:157—164, 1999 ISSN 1210-5759 Insect cold tolerance: How many kinds of frozen? B rent J. SINCLAIR Department o f Zoology, University o f Otago, PO Box 56, Dunedin, New Zealand; e-mail:
[email protected] Key words. Insect, cold hardiness, strategies, Freezing tolerance, Freeze intolerance Abstract. Insect cold tolerance mechanisms are often divided into freezing tolerance and freeze intolerance. This division has been criticised in recent years; Bale (1996) established five categories of cold tolerance. In Bale’s view, freezing tolerance is at the ex treme end of the spectrum o f cold tolerance, and represents insects which are most able to survive low temperatures. Data in the lit erature from 53 species o f freezing tolerant insects suggest that the freezing tolerance strategies o f these species are divisible into four groups according to supercooling point (SCP) and lower lethal temperature (LLT): (1) Partially Freezing Tolerant-species that survive a small proportion o f their body water converted into ice, (2) Moderately Freezing Tolerant-species die less than ten degrees below their SCP, (3) Strongly Freezing Tolerant-insects with LLTs 20 degrees or more below their SCP, and (4) Freezing Tolerant Species with Low Supercooling Points which freeze at very low temperatures, and can survive a few degrees below their SCP. The last 3 groups can survive the conversion of body water into ice to an equilibrium at sub-lethal environmental temperatures. Statistical analyses o f these groups are presented in this paper. However, the data set is small and biased, and there are many other aspects o f freezing tolerance, for example proportion o f body water frozen, and site o f ice nucleation, so these categories may have to be re vised in the future.